Method of using combustion adjuvant

ABSTRACT

A METHOD OF EMPLOYING AN ADJUVANT FOR HYDROCARBON FUELS IS PROVIDED BY ADDING AN ADJUVANT COMPRISING A CALCIUM BASED MONTMORILLONITE CLAY, A PHOSPHATE, AND A SOURCE OF BORON OXIDE TO A HYDROCARBON FUEL IN A COMBUSTION ZONE. A PREFERRED FORMULATION COMPRISES 85 WEIGHT PERCENT CALCIUM BENTIONITE, 10 WEIGHT PERCENT ANHYDROUS TRISODIUM PHOSPHATE, AND 5 WEIGHT PERCENT SODIUM BORATE. THE ADJUVANT IS COMBINED WITH THE HYDROCARBON FUEL OR WITH COMBUSTIONN AIR IN AN AMOUNT OF FROM ABOUT 0.00001 UP TO LESS THAN ABOUT 0.1 WEIGHT PERCENT, BASED ON THE WEIGHT OF THE HYDROCARBON FUEL. COMBUSTION EFFICIENCY IS SUBSWTANTIALLY IMPROVED AND OXIDATION IS SUBSTANTIALLY MORE COMPLETE, SO THAT COMBUSTION PRODUCTS ARE PRODUCED IN LESS NOXIOUS FORMS. IN ADDITION, THE NAATURE OF SLAG OR OTHER DEPOSITS UPON SURFACES IN A FURNACE OR COMBUSTION CHAMBER ARE SUBSTANTIALLY ALTERED, SO THAT CORROSIVE CONDITIONS DO NOT OCCUR AND THE DEPOSITION OF SLAG IS PREVENTED OR MATERIALLY REDUCED, AND THE ASH IS PRODUCED IN A SOFT, FRIABLE FORM.

United States Patent Int. Cl. C101 9/00, 1/32 U.S. Cl. 44-4 3 ClaimsABSTRACT OF THE DISCLOSURE A method of employing an adjuvant forhydrocarbon fuels is provided by adding an adjuvant comprising a calciumbased montmorillonite clay, a phosphate, and a source of boron oxide toa hydrocarbon fuel in a combustion zone. A preferred formulationcomprises 85 weight percent calcium bentonite, 10 weight percentanhydrous trisodium phosphate, and 5 Weight percent sodium borate. Theadjuvant is combined with the hydrocarbon fuel or with combustion air inan amount of from about 0.00001 up to less than about 0.1 weightpercent, based on the weight of the hydrocarbon fuel. Combustionefficiency is substantially improved and oxidation is substantially morecomplete, so that combustion products are produced in less noxiousforms. In addition, the nature of slag or other deposits upon surfacesin a furnace or combustion chamber are substantially altered, so thatcorrosive conditions do not occur and the deposition of slag is pre-'vented or materially reduced, and the ash is produced in a soft,friable form.

' This application is a continuation-in-part of applicants copendingapplication, Ser. No. 852,867, filed Aug. 25, 1969 now abandoned, andSer. No. 11,827, filed Feb. 16, 1970 (US. Pat. No. 3,628,925).

This invention relates to a method for employing an adjuvant forcombustion processes, and to a method for increasing the efliciencythereof. Additionally, the utilization of the method of this inventionsubstantially reduces the relative amounts of undesirable, harmful andtoxic components in the end products of hydrocarbon fuel combustion.

As is well known, the combustion of fuel oil, coal and natural gasproduces a large number of by-products, including dust, fly-ash, sulfurdioxide, etc. Incomplete combustion results in the discharge of smoke,soot and carbon monoxide into the atmosphere. Anticipated industrialexpansion threatens to increase the hazards of such air pollutionappallingly in the relatively near future. Such pollution adverselyaffects vegetative plants and the health of animals and humans. Suchefiects range from petty annoyance to chronic illness and death.

Polluted air has been linked to irritation of nose, throat, and eyes,aggravation of the respiratory tract, including bronchitis, emphysema,and cardiovascular ailments.

, Whether coal, gas, oil or other organic material comprises the fuel,with even the most efficient furnace design and operating conditions,complete combustion is seldom if ever attained. Build-up of tar, coke,soot and mineral slag on boiler surfacesconstitutes a serious problem,promoting chemical corrosion of metallic parts and greatly reducingefficiency of heat transfer. Burning of additional fuel to offset thisreduced heat transfer merely increases 3,738,819 Patented June 12, 1973the production of pollutants and adversely affects economy of operation.Furthermore, the procedures now commonly employed for removal of boilerdepots are costly, generally unsatisfactory, sometimes requiringshut-downs, and such practices as blow-off of soot and fly-ash areincreasingly prohibited by law.

Under conditions imposed by practical furnace construction, theformation of undesirable residues is a normal result of the combustionof fossil fuels. Except for the burning of elemental carbon, thecombustion comprises rapid chain reactions in the gas phase. Furnaceoperation can be described, in fact, as a controlled explosion. The typeand predominance of the various chain reaction steps depends partly uponthe type of fuel; but inasmuch as the principal ingredients are carbonand hydrogen, the process of burning is controlled more by externalfactors such as concentrations, initial gas temperature and manner ofmixing of fuel with the combustion air.

Majority of combustion occurs in the flame front, which measuresfractions of a millimeter in thickness. Whatever combustion occurs mustbe practically complete within this boundary between burned and unburnedgases, wherein all locally available oxygen is consumed. Underconditions of rapid furnace firing, ignition and combustion occur almostsimultaneously. Propagation of the flame front generally is a thermalprocess, in that the flame must transfer heat to the unburned gas tocause it to ignite.

In oil burners the fuel is either vaporized or atomized before ignition.On heating and vaporization, a certain amount of decomposition of suchoils occurs and some non-volatile carbonaceous material forms. Dropletsof heavy oils are partly carbonized within the flame. The tendency todeposit carbon on and around the burner is a function of both molecularweight and molecular structure of the fuel. Tendency of fuel oils tosmoke" increases with their carbon-hyrogen ratio.

Pulverized coal is 50% combusted in 0.05 second after the particlesleave the burner port. At 0.1 and 0.3 second, approximately 5% remainsunburned. Further reduction of unburned fixed carbon proceeds veryslowly; elementary carbon does not vaporize at ordinary flametemperatures.

The combustion flame front impinges on furnace Walls and other heatabsorbing surfaces, particularly under the conditions of hard firing.Although such surfaces may initiate some combustion steps throughproduction of free radical chain carriers, other combustionintermediates are destroyed by such contact. Additionally, in thepresence of insufficient air for complete combustion, lighter fractionsevaporate, but the more complex compounds decompose and formcarbonaceous deposits. Other factors contributing to carbon depositioninclude insuflicient secondary air, insuflicient mixing of air withvolatile matter, temperature of air and fuel falling below the criticaltemperature, insufiicient time of contact between air and fuel, orimpingement upon a cool surface. Incomplete secondary combustion resultsin formation of tarry vapors, solid carbon, gaseous hydrocarbons, carbonmonoxide and hydrogen. Finely divided carbon is swept away in suspensionin the flue gases to cooler zones of the furnace or is discharged fromthe stack as smoke or soot.

; Furnaces currently are constructed to provided for removal of depositsby blowers'and scrapers (or lances). Out-ofservice steam and waterwashing frequently is employed, although disposal of the wash wateroften becomes a problem. In-service boiler water washing can result indamage and should never be used with high-alloy super heater tubesbecause of thermal shock damage. tAlSO, chloride in the water caninitiate cracking of austenitic tubing.

Contributing to inefiiciency of furnace operations is deposition on thetubes of inorganic fuel ash. This slag not only creates resistance totransfer of heat energy, but is also generally acid in reaction, causingsulfuric acid corrosion of affected metal surfaces. Whereas coal ashtends to neutralize some of the acid formed in the boiler, the vanadiumcontained in most oils increases the formation of sulfuric acid fromsulfur dioxide. Consequently, the rapid removal of deposits on metalsurfaces is extremely important.

In view of the problems arising from furnace operation, there has beenan increasingly urgent need for means to enhance completeness ofcombustion, minimize formation of tarry and carbonaceous residues onboiler tubes and to prevent deposition of molten mineral slag on themetal surfaces.

It is accordingly an object of the present invention to provide a methodof employing an adjuvant for hydrocarbon fuels which increases theefficiency of combustion and alters the nature of the combustionproducts.

These and still other objects are realized by the method of using thecomposition of the combustion adjuvant in accordance with the presentinvention, comprising a calcium based montmorillonite, a phosphate, anda source of boron oxide. The calcium based montmorillonite constitutesat least about 75% weight percent of the adjuvant, while the phosphatemakes up about to 15 weight percent and the boron oxide sourceconstitutes about 1 to weight percent. In addition to the foregoing, theadjuvant can further include, if desired, an essentially inert diluentin amounts ranging from 0 up to several hundred, or even severalthousand weight percent, based on the weight of the adjuvant. As aninert diluent, any material can be used which does not detrimentallyhinder combustion or the functioning of the adjuvant. For example, thediluent can be a hydrocarbon fuel oil, a substantially inert solid, suchas a diatomaceous earth, or even an excess of the calcium basedmontmorillonite. The adjuvant composition is disclosed and claimed inthe aforesaid application, Ser. No. 11,827.

The calcium based montmorillonite is preferably one of the naturallyoccurring montmorillonite based clays, such as bentonite. The materialknown as Southern Bentonite is preferred, since it is readily availableat low cost in a form which is directly usable in the combustionadjuvant of the present invention, i.e. it is a calcium basedmontmorillonite. Other montmorillonite based clays can be used, butsince such materials are not ordinarily calcium based, it is necessarythat they be treated to replace at least a part of another metal withcalcium.

The term calcium based is used to indicate that a substantial proportionof the metallic ions replacing aluminum in the montmorillonitecrystalline lattice are calcium. The montmorillonite clays arecrystalline aluminosilicates of a specific, known composition, having aplanar structure of alternating sheets" of silica and alumina layerbonded to two silica layers. In other clays, such as kaolinite andillite, the structure differs by bonding of each silica layer to twolayers of alumina, while the montmorillonite has each silica layerbonded to one alumina layer and one silica layer. Thus, designatingsilica as Si and alumina by Al, the C-dimension of the montmorillonitecrystal lattice can be represented by the formula:

The adjacent i layers of the montmorillonite lattice gives the clay itsdistinctive properties.

Within the crystalline lattice of naturally occurring clays, a portionof the aluminum atoms are replaced by other metals in minor amounts,including iron, zinc, nickel, lithium, magnesium, calcium, potassium andsodium. In most montmorillonite clays of the bentonite variety, about 50to 75 milliequivalents of exchangeable metallic bases occur per 100grams of clay, and of this amount, sodium, calcium, magnesium and ironconstitute the bulk. The relative amounts of sodium and calcium are ofsignificance in the present invention, it being necessary to utilize amaterial having a predominant proportion of calcium and a relativelyminor proportion of sodium. The material commonly known as SouthernBentonite is suitable, having about 1.3 to 3.5 milliequivalents calciumand only about 0.3 to 0.45 milliequivalents sodium per 100 grams ofclay. Other clays of the montmorillonite type ordinarily predominate insodium, which is detrimental in the combustion adjuvant of the presentinvention, and such clays, if used, must be ion exchanged to removesodium and add calcium. The sodium content of the clay should not exceed1.0 weight percent. Since such manipulations add considerably to thecost of the product, it is preferred to use a calcium basedmontmorillonite of a naturally occurring variety, e.g. SouthernBentonite.

The phosphate component of the combustion adjuvant can be, insofar as ispresently known, any phosphate functional material, although some will,of course, be preferred for reasons of availability, cost or efliciency.For example, while in some contexts it will be desirable to utilizeorgano phosphates, e.g. tricresyl phosphate and the like, to reducedusting of the composition, in most circumstances, such materials willbe prohibitively expensive in comparison with inorganic phosphates.Common phosphate rock might be effective but for the highly corrosivenature of the hydrofluoric acid produced upon combustion. Preferred foreconomic considerations and effectiveness are the alkali metalphosphates, particularly anhydrous trisodium phosphate, which isinexpensive, readily available, and in a form conducive to ease ofhandling and formulation.

Similarly, the boron oxide can be supplied by any convenient source, solong as it does not further contain any constituent which is corrosiveor detrimental to combustion. Boron oxide per se can be used, but acheaper, more readily available source is sodium borate or common borax,which is accordingly preferred. Other alkali and alkaline earth metalborates and boric acid are further examples of suitable sources of theboron oxide.

The adjuvant composition is formed of the foregoing essential componentsas an intimate admixture in finely divided particulate form. Thematerials should be ground or pulverized to pass a 200 mesh, preferablya 325 mesh screen (to provide a maximum particle size of not more thanabout 44) The finer particle sizes enhance dispersion in the hydrocarbonfuel and minimize atomizer wear. The materials in such finely dividedform are often subject to dusting, which can be effectively prevented byincluding a minor amount of light oil or other suitable oiling agent.

The composition is effective in rather broad relative proportions of theessential components, with at least about 75 weight percent of thecalcium based montmorillonite being used, preferably about to 94 weightpercent, while the phosphate is preferably about 5 to 15 percent. Whencircumstances are appropriate, the essential components can be combinedwith varying amounts of an inert diluent. For example, when large scalefurnaces are utilized, their operation is often automated, and theintroduction of the adjuvant of the present invention is also desirablyautomated. Measurement, handling and distribution are often facilitatedby increasing the bulk of the adjuvant. The inert diluent can beutilized in amounts ranging from 0 to several hundred or even severalthousand, percent, e.g. 5,000%, based on the weight of the adjuvant. Thenature of such an inert diluent is limited only to materials which donot detrimentally afiect the operation of the furnace or of theadjuvant. Many such materials will be readily apparent to those ofordinary skill in the art, and can include, for example, both solid andliquid materials. For example, as illustrations of solid diluents whichcan be used, there can be mentioned coal, coke, carbon blacks,diatomaceous earth, siliceous materials, and the like. A particularlyadvantageous inert diluent is an excess of the calcium basedmontmorillonite. Liquid diluents can include such materials as kerosene,fuel oil, cycle oil, residual oils or the like.

The amount of the combustion additive to be added to a furnace will varywith the size and type of furnace and with the nature of the fuel. Theconsiderations vary greatly and no general rule can be given, althoughit has now been found that substantial degrees of effectiveness areattained when the adjuvant is employed at levels from as little as0.00001 up to less than about 0.1 weight percent, based on the Weight ofthe hydrocarbon fuel.

When the product of this invention, in finely ground form, is injectedinto the firing chamber, either independently, in intimate admixturewith the fuel, or in the combustion air, completeness of combustion inthe firebox is greatly enhanced, indicated by composition of stack gasesand lowering of stack temperature. Formation of smoke, soot and tars isgreatly reduced, and the deposition of slag and other materials on tubesand refractive surfaces is almost nullified. In fact, under properfiring conditions and without resort to mechanical cleaning methods,metal surfaces are maintained clean and bright. Accordingly, heattransfer is appreciably improved. Deposition of ash and slag isprevented almost entirely. Further, the slag removed from the ash pit isin a readily friable, powdery condition.

While the exact mode of operation of the composition is not clearlyunderstood, the following explanation is offered, but it should beunderstood that applicants do not wish to be bound thereby. The minutelyground material, mixed with the fuel as it is sprayed or injected intothe firing chamber, is broken into multitudinous finer particles at theflame front temperature. Heat energy absorbed by the crystallinematerial is surrendered and exchanged to combustion products as flamefront temperature decreases with flow through the furnace, therebypromoting more complete combustion. Whether added continuously orintermittently, the material of this invention, broken into particles bythe extreme temperatures, provides a very thin but frequently renewedhighly refractory surface, upon which unburned compounds impinge andthereby undergo further additional oxidative reaction.

In addition, it has been observed that the effect of the method of useof the combustion adjuvant is probably at least in part catalytic innature, although the precise nature of the catalytic effect has not beenascertained. The evidence supporting the probable catalytic nature ofthe effects of the present method are apparent from the followingexample, where it is clearly shown that the magnitude of the changesproduced by the method is far greater than could result fromstoichiometric effects alone.

EXAMPLE I A full scale test operation in an electric utility powerplant, in service to a small city, is conducted. The full scale test isconducted in a modern boiler which burns on the average, about fortythousand pounds per hour No. 6 fuel oil. The boiler is operated undernormal service conditions and monitored for the period of the test. Thetest program is conducted as follows:

The selected burner is removed from service, shut down and cleaning androutine maintenance are performed in the usual fashion. The furnace isthen started up and placed in service to base load generating equipmentunder normal operating conditions with a magnesium oxide anticorrosionadditive for about one month. When stable operating conditions areassured, base measurements, in

addition to the continuous monitoring by the operators, are taken. Threedays thereafter, injection of the adjuvant of Table I is started at arate of 0.023 weight percent based on the weight of the fuel, byinjection with service air. On the twenty-eighth day of injection datais again taken.

TABLE I 1 Wt. percent Calcium bentonite Trisodium phosphate (anhydrous)10 Sodium borate 5 The following results are obtained from the testperiod:

TABLE II Day Change percent (Base) 28 of base Adjuvant rate, wt. percent0 0.023 Sulfur content, fuel wt. percent (1 2. 25 2. 25 Fuel rate,percent base (1.) 96 -4.0 Air rate, percent base. 100 92 8. 0 Reheatertemp., F 990 1,010 +2.0 s03, p.p.m 22.1 8.2 64 502, p. .m 928.9 829.01l.0 00, v0 percent. i N.A. 0 a 100 002, vol. percent 12.2 13. 0 +6.0

1 Fuel rates and air rates are averages over the period of operation forthe boiler in service to base line generating capacity.

2 Base measurements of carbon monoxide were lost because of damage tothe samples taken.

a Carbon monoxide measurements were made by the Orsat system.

While Table II indicates substantial benefits to be derived from the useof the adjuvant, still other benefits accrue. For example, during theperiod of operation prior to injection of the adjuvant, relativelysubstantial amounts of slag and ash were produced, and deposits formedupon the surfaces of the furnace components. After a few hours ofcombustion with the adjuvant, slag and ash production was substantiallyreduced, and, additionally, the accumulated deposits were graduallyeliminated.

EXAMPLE H In a test furnace, the adjuvant of Example I, Table I, isemployed at a rate of about 0.00001 weight percent, based on the weightof fuel. Reductions in S0 SO ,CO, and fuel rate are noted.

As stated above, when bentonite is used as the silicate, it must be oflow sodium content, not more than 5% and preferably less than 1% asN320. Likewise, in order to preclude slagging, the bentonite shouldpossess not more than 10% by weight of iron, calculated as Fe O Shouldeither sodium or iron exceed the indicated maxima, these can be reducedin amount by partial pyroxying of the exchangeable bases with hydrogenions, utilizing acid treatment, or the like. Such procedure is familiarto those skilled in the art.

What is claimed is:

1. The method of promoting combustion efliciency of hydrocarbon fuelscomprising burning said fuels in a combustion zone and adding to saidcombustion zone about 0.0001 to less than about 0.1 weight percent,based on the weight of said fuel, of a combustion adjuvant comprisingabout 80 to 93 weight percent calcium montmorillonite, about 5 to 15weight percent of an alkali metal phosphate, and about 1 to 10 weightpercent of a source of boron oxide selected from the group consisting ofboron oxide, boric acid, alkali metal borates, and alkaline earthborates.

2. The method of claim 1 wherein said adjuvant is added to saidcombustion zone dispersed in combustion air.

3. The method of claim 1 wherein said adjuvant is added to saidcombustion zone dispersed in said fuel.

(References on following page) 7 8 References Cited 3,316,070 4/ 1967Scott 4451 3,628,925 12/ 1971 Milner 44-4 UNITED STATES PATENTS3,630,696 12/1971 Milner et a1 444 1/19'16 Barba 444 10/1940 Rick 61 5CARL F. DEES, Primary Examiner 10/ 1961 Thompson 444 10/ 1967 Kukin 444US. Cl. X.R. 11/1968 Booth 444

